Multi-circuit direct current monitor with modbus serial output

ABSTRACT

A multi-circuit direct current monitor consists of a plurality of Hall Effect current sensors mounted on a printed circuit board oriented to sense the direct current (DC) flow from power generating devices such as solar arrays, output from the Hall Effect sensors connected to an analog to digital (A/D) converter which in turn is connected to a microprocessor. The multi-circuit direct current monitor continuously monitors instantaneous and average current values for each circuit as well as total instantaneous current and average current for all active circuits. The multi-circuit direct current monitor provides continuous communications via Modbus RTU as well as providing alarm outputs if one or more circuits deviates from the average output by a percentage greater than the user specified threshold for a user-defined period of time to detect failed or underperforming power output devices.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. patent application Ser. No.12/288,956, filed Oct. 24, 2008, which application claims the benefit ofU.S. Provisional App. No. 60/984,497, filed Nov. 1, 2007.

BACKGROUND OF THE INVENTION

The present invention relates to a device for monitoring multiple DCelectrical currents using sensors and, more particularly, to a devicefor monitoring performance of multiple solar arrays with the sensors.This is referred to as Multi-Circuit Direct Current Monitor (MCDCM) forpurposes of this application.

Many commercial and institutional building owners are installing solararrays to provide electrical energy that can be used at the facilityand, in some cases, sold back to the utility providing power to thefacility. There are a number of elements that are monitored in thesesystems, both to measure the amount of power produced and consumed inthe facility and to ensure that the solar panels and arrays arefunctioning at peak efficiency. A typical large scale (>100 kilowatts)installation has a number of components that combine to produce usablepower at the facility level. The primary component of the installationis the solar panel which is a device composed of multiple individualphotovoltaic (PV) cells mounted in a weather-proof enclosure forinstallation on a roof top or other suitable location. Each of thesesolar panels produces a direct current (DC) power output from theradiation of the sunlight striking the panel. Typical power outputs forcommercial solar panels are in the range of 50 to >200 watts, withvoltages from 17 to 35 volts DC. For increased efficiency, multiplesolar panels are electrically connected into “strings” of up to 12individual panels to provide a single DC output for each string thatsums the power from each individual panel. The output from each of thesestrings is then wired into a combiner, which sums the power of multiplestrings into a single DC output. The DC power from the combiner (eithersingly or in series with other combiner boxes) is then sent to aninverter, which converts the DC output of the total solar array into 60Hz alternating current (AC) which can then be used by the facility forits power needs. In some cases, the facility owner may contract with itsexisting utility to sell the power back to the utility if there is solargenerating capacity that exceeds the needs of the facility itself.

For most commercial installations, the only required monitoring is themetering device that measures the AC power generated from the inverterof the solar array and the power consumed by the facility to meet itsneeds. This may require one or more meters to measure the bi-directionalflow of AC power and is generally referred to as a “net meter”, a termwhich simply refers to the ability of the meter(s) to measure the netamount of power consumed by the facility less the power produced by thesolar array (or other local generating sources such as generators). Thenet amount will be positive (i.e. the facility owes a dollar amount tothe utility) or negative (i.e. the facility has produced power in excessof its needs and is owed money from the utility for this production).These meters are generally specified by the utility in conjunction withthe installer and will provide outputs (generally Modbus or pulse) thatcan be monitored by the utility or a third party data acquisitionsystem. These meters are used for billing purposes, but they providelittle if any useful information about the operation of the strings orarrays of the solar system other than to provide a summary of the ACpower output from the inverter.

The purpose of the solar array is, of course, to provide power outputwhenever conditions are conducive to the production of power from theavailable sunlight. The theoretical maximum solar energy available is1000 W/m² (based on the amount of solar radiation at the equator at noonon an equinox day) and the efficiency of a PV cell is a measure of thepercentage of the maximum power potential and the actual output of thecell. For example, a PV cell with a 12% efficiency would produceapproximately 120 W/m² (1000 W/m²×12%) at noon at the equator on anequinox day. Most commercial PV panels in use today have ratedefficiencies of between 10% and 20%. The actual output of any givenpanel is affected by a number of factors, including the geographiclocation of the array, the angle of incidence, and the number of days ofsunshine. The output of the panel may also be impacted on a short termbasis by cloud cover, dirt, obstructions, or failure of any of theelectrical components or connections. The net meter previously describedcan only provide a general indication of the performance of the array,but cannot provide additional information regarding any of thecomponents in the overall solar system.

There are several external factors which may be measured in order todetermine if the solar array and its individual components arefunctioning properly and providing suitable power output. Environmentalindicators that may be monitored include (but are not limited to) thefollowing: solar radiance (in W/m²), temperature (in ° F. or ° C.),humidity (in % RH), wind speed (in miles/hour or km/hour), and winddirection. These can either be measured using individual sensorsconnected to an input/output module or the sensors may be incorporatedinto a weather station package that provides a serial output (e.g.Modbus RTU) that can be read by a computer or a data acquisition server.In the case of the weather station, the single serial output providesdata for each of the connected devices/components. Monitoring theseenvironmental factors allows the owner/installer to determine whatimpact (if any) changes in weather condition had on the expectedperformance of the solar array. For example, measuring the solarradiation (using a pyranometer) provides a basis for evaluating theimpact of smog or haze on the output of the solar arrays and the otherenvironmental factors can be considered in a similar manner to compareactual performance versus expected performance of the array.

The external environmental factors previously described can provideinsight into the performance of the solar array, but they do not providea means for locating and identifying other issues which may arise withinthe solar power system. Monitoring the inverter(s) on the solar systemcan provide information regarding the operation of the inverter itself,in particular the efficiency of the inverter in converting the incomingDC power into useful AC power. Tracking the input DC power and theoutput AC power (in conjunction with the weather monitoring systemdescribed previously) can help the owner/installer to identify problemsthat arise such as electrical failures or obstructions on the solararray as a whole, but does not provide information regarding the sourceof the inefficiency unless the inverter itself is at fault. For example,dirt or debris can accumulate on the surface of the solar panel and thiswill greatly reduce the amount of power produced by the panel as thesunlight is prevented from reaching the solar cell. This information canonly be gained by monitoring DC power output at the panel level or thestring level and using this data to determine if one or more panels arenot operating at expected efficiency. Monitoring of DC power at thestring level (typically 12 panels per string) provides sufficientaccuracy to permit identification of problems at the individual panel orstring that affect power output. This can be accomplished by usingindividual Hall Effect sensors or shunts to measure the DC current fromeach string, but this approach requires significant space forinstallation and also requires a number of additional devices andinstallation labor to bring each of the signals into an analog inputdevice for communication to the data acquisition system as well assignificant configuration labor to provide appropriate scaling factors.

What is desired, therefore, is a sensing device which provides DCcurrent sensing for multiple power feeds into a single device whichcontinuously measures the DC current from each string and provides anoutput for all desired parameters. This device may be suitable for bothnew installations and for retrofit into existing arrays afterinstallation has taken place. This device may be accurate enough toprovide indication of the failure of any PV cell in the string. Thedevice may also provide for a comparative analysis of the monitoredcircuits to provide indication of failed or failing panels based on athreshold of variance for one circuit from the value of other circuits,allowing for accurate reporting of failures across a wide spectrum ofsolar performance due to external factors (e.g. cloudy day).

The foregoing and other objectives, features and advantages of theinvention will be more completely understood upon consideration of thefollowing detailed descriptions of the invention, taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram of a typical commercial solar installation.

FIG. 2 is a detailed dimensional drawing.

FIG. 3 is a Modbus register list for the measured variables using the RS485 serial output.

FIG. 4 is a Modbus register list for system information parameters usingthe RS 485 serial output.

FIG. 5 is a diagram of a complete monitoring system for commercial solarphotovoltaic systems.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

Many commercial and institutional building owners are installing solarphotovoltaic systems to reduce their operating costs by generatingelectricity when sufficient solar energy is available and, in somecases, to sell power back to the utility when there is excess poweravailable from the solar system. In addition to the potential savingsand income generated from the solar system, there are significantincentives available from the utilities and from local, state andfederal government entities. Most of these installations are performedby contractors who specialize in solar projects, and these contractorsmay or may not provide guarantees of performance to the owners or mayshare in the savings generated. Regardless of who benefits from theinstallation of the solar generating system, the only way to increasethe return on investment (and recover the incentives) is to providemonitoring of operational parameters, both for the system as a whole andits component parts. If the system is not monitored on a “continuous”basis (or frequently), failures will occur that will not be identifiedin a timely manner and will result in a reduced return on investment.Most systems include weather monitoring equipment and metering systemsto measure the net flow of power, but these monitoring points areinsufficient to assist in identifying where problems are occurring. Adrop in expected power production from a failure of a string or panelcan not be corrected without extensive labor and downtime to isolate andidentify where the problem occurred. What is needed is a system formonitoring the performance of individual strings using devices which canidentify and communicate problems automatically, preferably usingindustry standard communications protocols. This device should becapable of installation in both new and existing solar generatingsystems without significant costs and should integrate “seamlessly” intoexisting monitoring systems.

Referring to FIG. 1, an exemplary commercial solar system and itscomponents is illustrated. A collection of solar PV panels 1 is selectedto meet the desired power output of the overall system (e.g. if thesystem is intended to produce 100 kilowatts of power, the system wouldbe specified for 500 panels with 200 watts of power per panel). Each ofthese individual solar panels are wired in series 16 with several otherpanels (typically eight to twelve panels) to form a PV string 2 whichsums the power output 18 from each of the panels. For example, if twelve200 watt panels are connected in a string, the power output from thestring would be 2400 watts. The output from this PV string is wired to acombiner box 5 with the outputs from other strings 14. The output fromeach of the PV strings 14 and 18 is inserted through the opening in oneof the sensors in the multi-circuit DC monitor (MCDCM) 4, providing atechnique of monitoring the DC current flow from each of the PV strings(detailed description of the operation of the multi-circuit DC monitoris provided elsewhere). Any suitable sensor may be used. Themulti-circuit DC monitor provides a serial port which allows multiplepoints to be read by the monitoring system from a single communicationsport utilizing a suitable protocol. One suitable protocol is the openModbus RTU protocol (see FIG. 5). The combiner box 5 performs severalancillary functions including safety and circuit protection; the primarypurpose of the combiner box is to provide a cumulative DC power output17 that is the sum of the inputs from all of (or a plurality of) thestrings 14 and 18.

The inverter 7 performs the function of converting the direct current(DC) power of the solar panels into three phase alternating current (AC)power which can be used by the facility to meet its power needs ascommercial power systems require three phase AC power (typically 208 Vor 480 V AC). The inverter accepts combined DC outputs from multiplecombiner boxes 17 which in turn take in multiple strings in the samemanner as described above for the combiner in FIG. 1. Each of theseadditional combiner boxes would have an MCDCM 4 to provide the samemonitoring as that shown in FIG. 1. The inverter typically utilizes aserial output 6 that provides information on operating parameters thatcan be monitored along with other components of the system to providetimely indication of system performance. The inverter serial outputs mayutilize Modbus RTU protocol to allow monitoring systems to read multipleparameters (e.g. DC input power, AC output power, inverter efficiency)from a single communication port (see FIG. 5). The three phase AC power8 leaves the inverter and is wired into the switchgear of the facility11 where the AC output of the solar system is matched to supply power ofthe facility 13 and, if applicable, to the utility grid 12. If thedemand of the facility for power is less than the power provided by thesolar system, the excess power can be sold back to the utility. If thedemand for power from the facility is greater than the power provided bythe solar system, the switchgear will draw the additional power requiredfrom the utility feeds 12.

The billing and reconciliation for the power used in the facility isaccomplished by a net meter 10. This net meter uses two sets of currenttransformers 9 connected to the net meter which measure the amperageflow from the solar system and into the facility. The net meter combinesthe amperage values from these current transformers with a voltageconnection to calculate the power in kilowatts that is provided from thesolar system and used by the facility. This net meter is usuallyconnected to a third party monitoring system to verify the powerproduced and purchased to reconcile the associated charges to and fromthe utility. Many net meters also provide an auxiliary communicationsoption (usually Modbus RTU) which can be monitored by the solarmonitoring system in FIG. 5.

Referring in detail to the drawings of the physical layout anddimensions of the multi-circuit DC monitor, referring in particular toFIG. 2, the MCDCM consists of a metal housing 24 with mounting tabs 21for installing the MCDCM. In a typical installation, the device ismounted inside an enclosure that meets the environmental requirementswhere the device is installed. The dimensions of the device allow for itto be installed inside a standard combiner box in either a newconstruction or retrofit installation. The primary sensing components ofthe device are preferable eight Hall Effect sensors 20 which provide fornon-contact sensing of DC current flows without the need for standardcurrent transducers or other current sensing components. The device ismounted in the combiner box or other enclosure such that the long edgeof the device is substantially perpendicular to direction of the wires26 carrying current from the solar PV strings. The wires from thestrings 26 are placed through the openings in the Hall Effect sensors,one conductor per sensor. The Hall Effect device measures the currentflowing in the conductor by measuring the effect of magnetic fieldgenerated from the current flowing in the conductor on a Hall Effectsensor mounted in a gap in the flux material of the device (the magneticfield generated by the current flow is proportional to the amount ofcurrent flowing in the conductor). Additional circuitry in the HallEffect sensor amplifies the low level signal generated by the Hallsensor to a 0 to 5 volt signal that can be read by a microprocessor.Hall effect sensors are preferably used for several reasons: first, theHall effect sensor is encapsulated to prevent dust or corrosion fromaffecting the accuracy; second, the Hall Effect sensor is non-intrusiveand thus provides and intrinsic barrier to the voltage being supplied onthe monitored conductor; third, the closed loop circuitry of the Halleffect sensor provides greater accuracy than other sensors; and finally,the Hall Effect sensor does not add resistance to the flow of thecurrent in the conductor as is the case with other sensor types such asshunts. The MCDCM provides two light emitting diodes (LED's) 27 and 25for power indication and serial transmission respectively. The MCDCM hasthree screw terminals 22 for connecting to a Modbus RTU serialcommunications network (terminals are +, −, and shield). The MCDCM hastwo terminals 23 for input power (24 VDC at 500 mA).

Referring in detail to the Modbus register list in FIG. 3 and FIG. 4,the instantaneous amperage value of each sensor input (Modbus registers40011 through 40018 inclusive) 32 is calculated by the ARM 7microprocessor in the following manner: the microprocessor of theinvention receives up to 32 sample readings from the ND converter foreach of the inputs and averages these 32 readings and updates theinstantaneous amperage value stored in the Modbus register for thechannel being read. This process is repeated for each of the inputchannels to update each of the Modbus register values on a continuousbasis. Each of these readings is stored as a twos complement, signedvalue.

In addition to the instantaneous amperage value for each input circuitoutlined above, the MCDCM maintains a “long average” for each channel,which is a calculated average for each channel over time (Modbusregisters 40019 through 40026) 33. This value is designed to provide theaverage of the instantaneous values for each channel for a particulartime interval selected by the user (e.g. 1 minute or 1 hour) to providea longer average period than the instantaneous. These values aretypically cleared by the data acquisition device by setting the Modbusregister 41017 44 to any value which clears all the long average values.

The MCDCM provides detection of a failed or underperforming circuit(e.g. a single solar panel in a string) by sending an output alarm viaModbus RTU if the instantaneous amperage of any of the 8 DC inputs fallsbelow a threshold established by the user. The MCDCM calculates theinstantaneous value from each of the Hall Effect sensors and compares itto the alarm deviation value set using Modbus register 41014 41 andstores the value as being in alarm if the instantaneous value is lessthan the minimum deviation in register 41014 41. If the instantaneousvalue has been in alarm for greater than the minimum time set in Modbusregister 41015 42, the MCDCM sets the alarm channel value in Modbusregister 40007 30 from 0 to 1-8 (depending on which channel is inalarm). This information will then be uploaded on the next request fordata from the Modbus master device on the RS 485 port.

Referring in detail to the Modbus register list in FIG. 4, in additionto the read-only registers described in FIG. 3 (Modbus registers 40001through 40026 inclusive) described previously, the MCDCM provides anumber of registers (all unsigned 16 bit integers) that contain systeminformation for the user and allow for programming input. Modbusregisters 41001 through 41003 34 are read only non-volatile registersthat contain serial number and calibration data. These values are set atthe factory and are not field programmable. Registers 41004 through41007 35 and 36 are also read-only non-volatile values set at the timeof production that contain the firmware version information andmanufacturing date. Modbus registers 41008 and 41009 37 are read-onlyregisters that monitor up-time (operating time) in the field in seconds.Registers 41011 and 41012 39 are read-only registers stored innon-volatile memory that provide information regarding the hardwareversion of the device and the printed circuit board revisionrespectively.

Modbus register 41010 38 is a read/write register that allows the uniqueModbus address to be written to the non-volatile memory. This Modbusaddress can be written to the register in the field allowing the user toassign an address that does not conflict with other Modbus devices onthe same network.

Register 41013 40 is a read/write register that stores the minimumthreshold for alarm values. This allows the user to eliminate “nuisance”alarms by disabling the alarm deviation feature if the instantaneouscurrent falls below the level set in register 41013 40. Register 4101441 is a read/write non-volatile value that establishes the minimum alarmthreshold as a percentage of the instantaneous total current calculatedin registers 40001 and 40002 28. This value can be changed by the userto set a threshold that corresponds to actual conditions. Register 4101542 is also a read/write non-volatile value that contains the minimumtime (in seconds) that a particular channel needs to be in alarm beforethe alarm register 40007 30 is set to an alarm condition. This value canbe modified by the user to meet the needs of the particular circuitsbeing monitored. Register 41016 43 is a read/write non-volatile registerthat allows the user to disable monitoring of instantaneous amperagevalues for any channels, allowing the user to minimize nuisance alarmsfor any channels that are not used either temporarily or permanently.Register 41017 44 is a write only value that clears all long averagevalues (Modbus registers 40003-40004 28 and 40019-40026 33). This allowsthe user to clear average values at the end of a log cycle (if desired)and to initiate a new long average calculation.

Referring in detail to the solar monitoring system shown in FIG. 5, theMCDCM 4 is shown as it would be used in a typical Modbus dataacquisition system for logging and monitoring solar array performance.In this image, the DC output 14 of the solar photovoltaic strings 2 ismonitored by the MCDCM 4 as they enter the combiner box 5 as describedin detail previously. Serial communications with the MCDCM's isaccomplished using a twisted pair of wires 49 carrying the Modbusprotocol transmission from the master data acquisition device 48 whichalso queries other Modbus devices (e.g. the inverter 7 or a Modbusweather station 46 on user-selected intervals). Data from the Modbusdevices is transmitted using either twisted pair wires 49 or wirelesslyusing wireless Modbus transceivers 45, 47 to send data on a mesh radionetwork 50 where wiring is not practical or cost-effective.

In a typical installation, the data acquisition system functions in thefollowing manner:

-   -   1. The data acquisition master device 48 initiates a request for        Modbus register data from one or more connected Modbus devices        using the master wireless mesh transceiver 47 to send the        request wirelessly to other transceivers 45 and then to the        Modbus device (e.g. MCDCM 4 or inverter 7).    -   2. The MCDCM 4 (or other Modbus device) responds to the request        by sending the value(s) stored in the requested register(s)        using the same communications chain to the data acquisition        device 48 which stores or forwards the data to a remote database        server for long-term storage and display.    -   3. The data acquisition device 48 typically time stamps the        received Modbus data and stores it in non-volatile memory till        an upload request is received (upload may be automatic based on        time parameters stored in the data acquisition device).    -   4. At this point, the data is converted to an open format (HTTP,        xml, among others) and is communicated via the internet using        either a local area network (LAN), phone line or a cellular        network.

The data acquisition device can also provide near real-time data fromany of the Modbus devices when a request is made from an external laptopor PC running a web browser if the external device is on a sub-net withthe data acquisition device.

The terms and expressions which have been employed in the foregoingspecification are used therein as terms of description and not oflimitation, and there is no intention, in the use of such terms andexpressions, of excluding equivalents of the features shown anddescribed or portions thereof, it being recognized that the scope of theinvention is defined and limited only by the claims which follow.

We claim:
 1. A method for monitoring direct current (DC) supplied by asolar photovoltaic system including a plurality of solar panels; themethod comprising the steps of: (a) providing a multi-circuit directcurrent monitor (MCDCM) having a microprocessor and a plurality ofsensors; (b) coupling each of the sensors of the MCDCM to one of theplurality of solar panels; (c) monitoring an instantaneous current valuefor each sensor; (d) monitoring a long average current value for eachsensor; (e) with said microprocessor, comparing the instantaneouscurrent value for each sensor against the long average current value foreach respective sensor; (f) sending an output alarm if the instantaneouscurrent value for any one of the sensors deviates from the long averagecurrent value for each respective sensor by a threshold value; (g) withsaid microprocessor calculating, for each of the sensors, an averagecurrent value of the long average current value of the remainingsensors; (h) with said microprocessor, comparing the long averagecurrent value for each of the sensors against the average current valueof the long average current value of the remaining sensors; and (i)sending an output alarm if the long average current value for any one ofthe sensors deviates from the average current value of the long averagecurrent value of the remaining sensors by the threshold value.
 2. Themethod of claim 1 wherein the instantaneous current value for eachsensor is calculated by the microprocessor via averaging a plurality ofreadings of the current for each sensor, wherein the number of readingsfor the instantaneous current is less than a number of readings used tocalculate the long average current value for each sensor.
 3. The methodof claim 1, wherein step (d) comprises maintaining an average currentvalue for each sensor for a particular time interval as selected by auser.
 4. The method of claim 1, wherein the microprocessor stores thethreshold value.
 5. The method of claim 4, wherein the threshold valueis a minimum instantaneous current threshold.
 6. The method of claim 4,wherein the threshold value is a deviation percentage value of theinstantaneous total current.
 7. The method of claim 6, wherein thepercentage value can be modified by a user.
 8. The method of claim 4,wherein the output alarm is sent only if the instantaneous current valuefor any one of the sensors falls below the threshold value for apredetermined time duration.
 9. The method of claim 8, wherein thepredetermined time duration is set by a user.
 10. The method of claim 1,further comprising enabling the user to disable the output alarm. 11.The method of claim 1, further comprising enabling the user to disablemonitoring an instantaneous current value for any one sensor.
 12. Themethod of claim 1, wherein the microprocessor maintains a bitmap foreach sensor so that each sensor can be selectively enabled by the user.13. The method of claim 1, wherein the long average current value iserased based on a time period determined by the user.
 14. The method ofclaim 1, wherein the microprocessor includes system information.
 15. Themethod of claim 14, wherein the system information includes factory setserial number and calibration data for the MCDCM.
 16. The method ofclaim 14, wherein the system information includes firmware versioninformation.
 17. The method of claim 14, wherein the system informationincludes factory set time of production information includingmanufacturing date of the MCDCM.
 18. The method of claim 14, wherein thesystem information includes total amount of up time for the MCDCM. 19.The method of claim 14, wherein the system information includes Modbusaddress.
 20. The method of claim 14, wherein the system informationincludes hardware version information and print circuit board (PCB)version number information.
 21. The method of claim 1, wherein each ofsaid sensors is a Hall Effect current sensor, each of said Hall Effectcurrent sensors includes an aperture so that a wire carrying currentfrom the respective solar panels is inserted through the aperture in theHall Effect current sensor.
 22. The method of claim 21, wherein theMCDCM is rectangular having a length longer than a width and the MCDCMis mounted such that the length of the MCDCM is substantiallyperpendicular to a direction of the wires carrying current from thesolar panels.
 23. The method of claim 1, wherein each of said sensorscommunicates with another device using a single communications port. 24.The method of claim 23, wherein said communications port is an RS-485serial port.
 25. The method of claim 24, wherein said serial portcommunicates with said another device using Modbus RTU protocol.
 26. Themethod of claim 1, wherein the plurality of solar panels areelectrically connected to one another to form a photovoltaic string, andeach of the sensors of the MCDCM is connected to one of the plurality ofphotovoltaic strings so that each of the sensors monitors the sum of thedirect current (DC) supplied by the photovoltaic string.
 27. The methodof claim 1, further comprising the step of connecting the MCDCM to aModbus RTU serial communications network.
 28. A method for monitoringdirect current (DC) supplied by a solar photovoltaic system including aplurality of solar panels; the method comprising the steps of: (a)providing a multi-circuit direct current monitor (MCDCM) having amicroprocessor and a plurality of sensors; (b) coupling each of thesensors of the MCDCM to one of the plurality of solar panels; (c)monitoring an instantaneous current value for each sensor; (d)monitoring a long average current value for each sensor; (e) with saidmicroprocessor, comparing the instantaneous current value for eachsensor against the long average current value for each respective sensorwherein the instantaneous current value for each sensor is calculated bythe microprocessor via averaging a plurality of readings of the currentfor each sensor, wherein the number of readings for the instantaneouscurrent is less than a number of readings used to calculate the longaverage current value for each sensor; and (f) sending an output alarmif the instantaneous current value for any one of the sensors deviatesfrom the long average current value for each respective sensor by athreshold value.
 29. The method of claim 28, wherein step (d) comprisesmaintaining an average current value for each sensor for a particulartime interval as selected by a user.
 30. The method of claim 28, whereinthe microprocessor stores the threshold value.
 31. The method of claim30, wherein the threshold value is a minimum instantaneous currentthreshold.
 32. The method of claim 30, wherein the threshold value is adeviation percentage value of the instantaneous total current.
 33. Themethod of claim 32, wherein the percentage value can be modified by auser.
 34. The method of claim 30, wherein the output alarm is sent onlyif the instantaneous current value for any one of the sensors fallsbelow the threshold value for a predetermined time duration.
 35. Themethod of claim 34, wherein the predetermined time duration is set by auser.
 36. The method of claim 28, further comprising enabling the userto disable the output alarm.
 37. The method of claim 28, furthercomprising enabling the user to disable monitoring an instantaneouscurrent value for any one sensor.
 38. The method of claim 28, whereinthe microprocessor maintains a bitmap for each sensor so that eachsensor can be selectively enabled by the user.
 39. The method of claim28, wherein the long average current value is erased based on a timeperiod determined by the user.
 40. The method of claim 28, wherein themicroprocessor includes system information.
 41. The method of claim 40,wherein the system information includes factory set serial number andcalibration data for the MCDCM.
 42. The method of claim 40, wherein thesystem information includes firmware version information.
 43. The methodof claim 40, wherein the system information includes factory set time ofproduction information including manufacturing date of the MCDCM. 44.The method of claim 40, wherein the system information includes totalamount of up time for the MCDCM.
 45. The method of claim 40, wherein thesystem information includes Modbus address.
 46. The method of claim 40,wherein the system information includes hardware version information andprint circuit board (PCB) version number information.
 47. The method ofclaim 28, wherein each of said sensors is a Hall Effect current sensor,each of said Hall Effect current sensors includes an aperture so that awire carrying current from the respective solar panels is insertedthrough the aperture in the Hall Effect current sensor.
 48. The methodof claim 47, wherein the MCDCM is rectangular having a length longerthan a width and the MCDCM is mounted such that the length of the MCDCMis substantially perpendicular to a direction of the wires carryingcurrent from the solar panels.
 49. The method of claim 28, wherein eachof said sensors communicates with another device using a singlecommunications port.
 50. The method of claim 49, wherein saidcommunications port is an RS-485 serial port.
 51. The method of claim50, wherein said serial port communicates with said another device usingModbus RTU protocol.
 52. The method of claim 28, wherein the pluralityof solar panels are electrically connected to one another to form aphotovoltaic string, and each of the sensors of the MCDCM is connectedto one of the plurality of photovoltaic strings so that each of thesensors monitors the sum of the direct current (DC) supplied by thephotovoltaic string.
 53. The method of claim 28, further comprising thestep of connecting the MCDCM to a Modbus RTU serial communicationsnetwork.
 54. The method of claim 28, further comprising the steps of:(a) with the microprocessor, calculating, for each of the sensors, anaverage current value of the long average current value of the remainingsensors; (b) with the microprocessor, comparing the long average currentvalue for each of the sensors against the average current value of thelong average current value of the remaining sensors; and (c) sending anoutput alarm if the long average current value for any one of thesensors deviates from the average current value of the long averagecurrent value of the remaining sensors by the threshold value.